1. Field of the Invention
This invention relates to mobile telecommunications systems and, more particularly, to a system for integrating a private mobile telecommunications system into a public mobile telecommunications network.
2. History of the Prior Art
Recent advances in mobile telecommunications have resulted in a variety of services that may be provided to a mobile subscriber. These services include both private services usually provided within a business environment for private mobile subscribers and public services provided through a public land mobile network for public mobile subscribers. Both private and public mobile service may be provided on a cellular basis, with mobile subscribers being allowed to roam between the coverage areas of different base stations of each of the private and public systems.
Private mobile service is typically provided through a private mobile telephony network that is implemented using a private cordless system standard such as the Cordless Telephone Standard 2 (CT-2) or, the digital European Cordless Telephone Standard (DECT). Private telephony networks are either provided as stand alone systems or, connected to a fixed telephony network. The private mobile telephony network is commonly used to provide mobile service within a single building or office complex of a business.
Public mobile service is typically provided through a cellular telecommunication network implemented using one of the common cellular systems standards such as the Advanced Mobile Phone Service (AMPS) System Standard, the IS-54 Time Division Multiple Access (TDMA) Standard, or the European Groupe Speciale Mobile (GSM) Standard.
The demand for public cellular telecommunication networks to also support indoor or office locations, such as those supported by a private telephony network, has grown the last few years. This demand however, has been largely unsatisfied even though several types of solutions have been implemented in the industry.
A solution using public cellular networks together with private telephony networks that are provided as stand alone or, are connected to a fixed private telephony network, does not allow roaming between the private network and public network. A solution of this type using private cordless systems within indoor and office locations is therefore not able to provide mobile service with roaming in a public cellular network. A second type of solution has been developed that provides service through a public cellular system having indoor coverage and a customized intelligent network service for corporate groups subscribing to the public cellular system. This allows mobile subscribers to use the same mobile station when operating in either the corporate environment or the public network. This service, however, is still a public service provided by the cellular system and, the indoor network is under the control of the cellular system operator. Also, in this type of solution, there may be poor integration of the corporate services into the public cellular system. For example, the presentation of a corporate extension number at a mobile station as a dialed number (A-number) may not be possible. Desktop and mobile stations will also belong to different networks and may provide different services, causing confusion for users. Additionally, corporate management systems for monitoring and tracking will not have the ability to trace and monitor calls that involve members of the corporate group using a mobile station.
A third type of solution uses dual mode mobile stations, e.g., a mobile station capable of operating in both a GSM or DECT system. This type of solution overcomes some of the drawbacks with the previously mentioned solutions. However, a dual mode mobile station user will be provided a different set of services when using the DECT system than then operating on the public cellular system. Also, private to public system seamless handover is not possible and dual mobile stations are complex and, therefore more expensive.